This invention relates to an illuminance distribution measuring method and exposing method, which are applicable to an exposure apparatus for performing the exposure of pattern of semiconductor element or liquid crystal display element in the step of photolithography.
In view of the increasing demand for semiconductor element as well as for the reduction of manufacturing cost of semiconductor element in recent years, it is now desired to enhance the throughput of an exposure apparatus to be employed in the manufacture of semiconductor element, etc. According to an exposure apparatus of this kind, a circuit pattern formed on a projection original (hereinafter generically referred to as reticle) such as a reticle and mask is illuminated by a luminous flux from an optical illumination system, and the pattern thus illuminated is then transferred as an image, by making use of a projection type optical system, onto a photosensitive substrate (hereinafter referred to simply as a substrate) such as a glass plate or wafer having thereon a coated layer of photosensitive material such as resist. Under the circumstances, there has been developed a technique to shorten the exposure time by increasing the illuminance at the surface of the substrate, thereby enhancing the throughput of the exposure apparatus.
Meanwhile, the adjustment in quantity of exposure to the surface of substrate in the exposure apparatus of this kind is performed as follows. Namely, a photoelectric sensor provided with a pin-hole plate to be positioned at the same level as that of the surface of substrate is placed on a substrate stage for mounting the substrate in the vicinity of the location where the substrate is to be positioned. Then, the photoelectric sensor is moved to the irradiation region or exposure region of illuminating light. More specifically, as shown in FIG. 8, the photoelectric sensor is moved step by step from the measurement starting position P1 to the measurement finishing position Pm within the exposure region 50. The measurement of illuminance is performed once at each position starting from the starting position P1 to the finishing position Pm, thereby obtaining the illuminance distribution of the exposure light. Based on the results of measurement, the magnitude of illuminance and irradiation time (in the case of pulse beam, the number of pulse) of the exposure light are controlled, thereby adjusting the quantity of exposure to the surface of substrate.
However, when the illuminance of the exposure light onto the surface of the substrate is increased, the light irradiation energy onto the substrate is increased, thereby inviting a rise in temperature of the photoelectric sensor per se that has been placed within the exposure region. As a result, the output to be obtained by the photoelectric sensor is influenced by a drift due to this temperature increase. In particular, in the case of a reduction projection type exposure apparatus, since the photoelectric sensor which is designed to measure the uniformity of illuminance (or illuminance irregularity) at the surface of substrate is inevitably exposed to an intense exposure light, the photoelectric sensor is suffered from a large quantity of heat. Therefore, in the conventional method where the photoelectric sensor is moved while stopping at every measurement position within the exposure region thereby to intermittently measure the illuminance of measurement positions, the illumination heat is gradually accumulated in the photoelectric sensor with time, thereby inviting a tendency that the later the time of measurement is, the larger the degree of increase in output (measured value) over the actual illuminance due to a drift. As a result, there is a problem that the measured value is caused to include an illuminance irregularity which is not inherently originated from an optical illumination system and a projection type optical system.